Cancers are like uncontrolled pathogens. They multiply and spread up to the point of killing their host. Naturally our immune system protects us not only from pathogens but also from cancers. Indeed, cancer immunotherapy has been an effective therapy against many cancers. However, the underlying mechanisms in many cases are poorly understood. Type I interferon (IFN) and anti-tumor T cells are vital in controlling immunogenic tumors. IFN signaling in dendritic cells (DCs) is crucial for cross-priming of T cells against tumors. DCs mediates the immune recognition of tumors via cytosolic DNA sensing pathway and subsequent production of IFN from the DCs. It is unclear, however, how immunogenic tumors induces IFN production from DCs through the cytosolic DNA sens- ing pathway and how IFN signaling in DCs is necessary for the cross-priming of T cells. While studying host- pathogen interactions, we discovered a novel function of autophagy proteins that can provide answers to these questions. Autophagy is an evolutionarily conserved cellular pathway that encloses cytoplasmic materials in membrane-bound autophagosomes and delivers them to the lysosome for degradation. The autophagosomes form from endomembranes reorganized via the ubiquitin-like conjugation system of the autophagy pathway. We found that the conjugation system plays another essential role in the disintegration of intracellular vacuoles con- taining pathogens by tagging the vacuoles with ubiquitin-like LC3 (microtubule associated protein 1 light chain 3). The membrane bound LC3s function as molecular beacons to recruit IFN-inducible GTPases, and the re- cruited GTPases disrupt the vacuoles. As a result, the pathogens hidden inside the vacuole are exposed to the cytoplasm. We hypothesize that the same LC3 conjugation system in DCs opens up phagocytic vacuoles con- taining tumor cell DNAs and antigens by recruiting the IFN-inducible GTPases to the vacuoles. Subsequent release of the contents to the cytoplasm of the DCs will lead to cytosolic DNA sensing-dependent IFN production (positive amplification of IFN signal) and the cross-priming of cytotoxic T cells against the tumor cells. To test this hypothesis, we will investigate the role of the relevant autophagy genes and the IFN-inducible GTPases in DCs for the production and amplification of IFNs, the cross-priming of cytotoxic T cells against tumor antigens, and the control of immunogenic tumors in vivo. Successful completion of the proposed study will lead to a better understanding of innate and adaptive immune recognition of tumors. Such results are expected to have positive impact on human health because it is probable that the identified immune regulatory mechanism will provide new targets for therapeutic interventions of cancers. In addition, it is likely that the result will enhance our under- standing of how the immune system controls cytosolic vacuoles containing materials of interest (e.g. pathogens, tumors, etc.), thereby fundamentally advancing the fields of cancer biology, immunology and cell biology. Fur- ther, the targeting mechanism may be utilized for other process, like controlled drug delivery. In essence, this is a high-risk/high-reward project.